Onyx Lounge in DTLA For 30th Birthday
Never been to Onyx Lounge but there are a ton of bars nearby. Here's just a few I've tried/heard of.
The Varnish is one of my favorite places for a drink -- a dark speakeasy -- but it's tiny and certainly not good for large crowds.
Perch is a bit more of a walk -- haven't tried it but have heard only good things. Not sure you can go wrong with a nice rooftop setting that offers great city views. Definitely get a res way in advance.
The Down and Out is always a good time. Pool, loud music, and mug shot photos.
Seven Grand has a line out the door most times I pass it. My partying friends like it, haven't been myself.
Hope that gets you started in your research.